AHA! "Petloader" are the ones i was trying to find the other day!
Dog Steps, Dog Stairs and Dog Ramps from Pet Loader
What about a block of foam (like several sheets of that construction insulation cut to a step-sized piece and glued together) covered with some inexpensive thin carpet? a friend made a 2-step one for the back of her Kia minivan, the bottom is a rectangle, the top one is square, they velcro together. each piece was about 7" high, and they weigh next to nothing. She said they work great in motels for the dogs to get up to the bed too. With your car side height, you may be able to get away with one piece, kind of like a mounting block but with only one piece.